I'm not sure if others will agree, but when I've tried to teach folk to read basic #Gàidhlig I would describe H as the "magic letter" or symbol that performs functions (lenition)

Tha - The H makes the T disappear - Read Ha.

Shona - The H makes S disappear - becomes Hona

Etc

You're never going to see the magic letter on its own unless it's a loanword or a Norse placename, so any time you see the letter H in a word you know it's serving a function.

Bearing in mind at one point it was even just a wee dot above the letter...

Take this Irish example

Ċuaiġ bé ṁórṡáċ le dlúṫspád fíorḟinn trí hata mo ḋea-ṗorcáin ḃig

This reads:

Chuaigh bé mhórshách le dlúthspád fíorfhinn trí hata mo dhea-phorcáin bhig

Tha gu math

If you imagine the H is causing the T's to disappear, what do you get?

Ha gu mah